Broad-band polarization-independent metamaterial absorber for solar energy harvesting applications

A novel broad-band polarization-independent with wide-angle metamaterial absorber(MA) is investigated and demonstrated for solar energy harvesting applications. The proposed MA is composed of two metal layers which have different thickness and a dielectric layer which is sandwiched between these metal layers. By this combination, the proposed MA indicates plasmonic resonance characteristic. Numeric results show that proposed MA has perfect absorption characteristic which is above 88.28% with wide-angle for all visible region. It shows almost perfect absorption of 98.4% at the resonance frequency of 621.76 THz and has also 90% absorption between frequencies of 445 THz and 770 THz which is nearly all visible light region. Besides, numerical results validate that the proposed MA could achieve very high absorption at wide-angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.. The proposed MA and its variations enable for solar cell applications due to have upper ratio of 90% in the widest range of visible spectrum comparing to the studies in literature. In order to show additional features of the proposed structure, parametric studies are realized and discussed. Furthermore, the absorption characteristic of proposed MA is investigated for infrared and ultraviolet region. The enhancement of absorption of the structure will provide new type of sensors in these frequency ranges.     

Preparation, characterization, and theoretical studies of azelaic acid derived from oleic acid by use of a novel ozonolysis method

Environmentally friendly manufacture of organic compounds has been intensively reexamined in recent years. Many excellent methods have been devised to produce organic compounds from renewable resources. Azelaic acid has been produced by ozonolysis of oleic acid. The reaction was performed in a Bach bubbling reactor, with fine bubbles, at high temperature (150 °C) without utilizing any catalyst or any solvent. Yield of the reaction was 20% after 2 h. Production of azelaic acid was confirmed by use of FT-IR and ¹H NMR spectroscopic data and high-performance liquid chromatography of both synthesized and reference azelaic acid. A theoretical study was performed to obtain quantum chemical data for azelaic acid and to optimize the molecule’s geometry.     

Reduction of hexavalent chromium with colloidal and supported palladium nanocatalysts

Zinc oxide (ZnO) nanowires (NWs) are exposed to energetic proton (H⁺), nitrogen (N⁺), phosphorus (P⁺), and argon (Ar⁺) ions to understand the radiation hardness and structural changes induced by these irradiations. High-resolution transmission electron microscopy is utilized to see the irradiation effects in NWs. Multiple doses and energies of radiation at different temperatures are used for different set of samples. The study reveals that wurtzite (crystalline)-structured ZnO NWs experience amorphization, degradation, and morphological changes after the irradiation. At room temperature, deterioration of the crystalline structure is observed under high fluence of H⁺, N⁺, and P⁺ ions. While for ZnO NWs, bombarded by Ar⁺ and P⁺ ions, nano-holes are produced. The ZnO NWs surfaces also show corrugated morphology full of nano-humps when irradiated by Ar⁺ ions at 400 °C. The corrugated surface could serve as tight-holding interface when interconnecting it with other NWs/nanotubes. These nano-humps may have the function of increasing the surface for surface-oriented sensing applications in the future.     

Influence of the physico-chemical properties of Selangor soil series on the distribution coefficient (<Emphasis Type="Italic">K</Emphasis><Subscript>d</Subscript>-value) of <Superscript>226</Superscript>Ra

²²⁶Ra is a member of the ²³⁸U natural decay series and is one of the most important isotope to be determined among the naturally occurring nuclides in environmental samples. In order to evaluate the radiation dose from ²²⁶Ra, it is important to know its mobility in different types of soils. The aim of the present study is to quantify the influence of physico-chemical soil properties on ²²⁶Ra adsorption. The distribution coefficients (K _d-value) of ²²⁶Ra in Selangor soil series samples were measured in one core, at three depth levels to evaluate the adsorbability of ²²⁶Ra. The soil samples were spiked with ²²⁶Ra tracer and the activities of ²²⁶Ra in the separated phase from batch sorption test were measured by a low background but high efficiency well-type HPGe detector. Several physico-chemical soil properties were also characterised for each soil samples. Pearson’s correlation and stepwise multiple regression test were applied at the 0.05 level of significance throughout all analysis to determine the relationships and influences between distribution coefficients (K _d-value) of ²²⁶Ra with physicochemical soil properties for the Selangor soil series. The observed K _d value was in the range of 50.55–172.28 mL g⁻¹ (mean: 93.20 ± 46.99 mL g⁻¹). The regression showed that the highest positive correlations were observed for organic matter (OM) and cation exchange capacity (CEC) (r = 0.96**, 0.81**, respectively) with K _d-values. The results indicate that the stepwise multiple regression model incorporating the soil’s OM and CEC accounts for 98% of the variability in distribution coefficients of ²²⁶Ra.     

Robust active sliding mode anti-synchronization of hyperchaotic systems with uncertainties and external disturbances

In this paper, we demonstrate that anti-synchronization can coexist in two different hyperchaotic systems with terms of parametric uncertainty and external disturbances using the robust active sliding mode control method. By using rigorous mathematical theory, the sufficient condition is drawn for the stability of error dynamics based on the Lyapunov stability theory, where the controllers are designed by using the sum of the relevant variables in hyperchaotic systems. Numerical results are presented to justify the theoretical analysis.     

MHD mixed convection flow near the stagnation-point on a vertical permeable surface

The steady magnetohydrodynamic (MHD) mixed convection boundary layer flow of a viscous and electrically conducting fluid near the stagnation-point on a vertical permeable surface is investigated in this study. The velocity of the external flow and the temperature of the plate surface are assumed to vary linearly with the distance from the stagnation-point. The governing partial differential equations are first transformed into ordinary differential equations, before being solved numerically by a finite-difference method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both assisting and opposing flows are considered. It is found that dual solutions exist for both cases, and the range of the mixed convection parameter for which the solution exists increases with suction.     

Liquid Film on Unsteady Stretching Sheet with General Surface Temperature and Viscous Dissipation

We study the effects of viscous dissipation on flow and heat transfer in a thin liquid film on an unsteady stretching sheet. A general surface temperature is taken into consideration. The velocity and temperature fields are solved using the homotopy analysis method. The results show that the increasing values of the Eckert number can increase temperature distribution and the heat transfer rate.     

Influence of growth morphology on the Néel temperature of CrRu thin films and heterostructures

Dimensionality effects on epitaxial and polycrystalline Cr_1?xRu_x alloy thin films and in Cr/Cr–Ru heterostructures are reported. X-ray analysis on Cr_0.9965Ru_0.0035 epitaxial films indicates an increase in the coherence length in growth directions (1 0 0) and (1 1 0) with increasing thickness (d), in the range 20≤d≤300 nm. Atomic force microscopy studies on these films shows pronounced vertical growth for d>50 nm, resulting in the formation of columnar structures. The Néel temperatures (T_N) of the Cr_0.9965Ru_0.0035 films show anomalous behaviour as a function of d at thickness d≈50 nm. It is interesting to note that this thickness corresponds to that for which a change in film morphology occurs. Experiments on epitaxial Cr_1?xRu_x thin films, with 0≤x≤0.013 and d=50 nm, give T_N–x curves that correspond well with that of bulk Cr_1?xRu_x alloys. Studies on Cr/Cr_0.9965Ru_0.0035 superlattices prepared on MgO(1 0 0), with the Cr layer thickness varied between 10 and 50 nm, keeping the Cr_0.9965Ru_0.0035 thickness constant at 10 nm, indicate a sharp decrease in T_N as the Cr separation layers reaches a thickness of 30 nm; ascribed to spin density wave pinning in the Cr layers for d<30 nm by the adjacent CrRu layers.     

Radiation Effects on the Flow and Heat Transfer over a Moving Plate in a Parallel Stream

Effects of thermal radiation on the steady laminar boundary layer flow over a moving plate in a moving fluid is investigated. Under certain conditions, the present problem reduces to the classical Blasius and Sakiadis problems. It is found that dual solutions exist when the plate and the fluid move in the opposite directions. Moreover, the existence of thermal radiation is to reduce the heat transfer rate at the surface.     

MHD stagnation point flow towards a stretching sheet

The steady two-dimensional MHD stagnation point flow towards a stretching sheet with variable surface temperature is investigated. The governing system of partial differential equations are transformed into ordinary differential equations, which are then solved numerically using a finite-difference scheme known as the Keller-box method. The effects of the governing parameters on the flow field and heat transfer characteristics are obtained and discussed. It is found that the heat transfer rate at the surface increases with the magnetic parameter when the free stream velocity exceeds the stretching velocity, i.e. ε>1, and the opposite is observed when ε<1.